1. Technical Field
The present invention generally relates to imaging an object with electromagnetic radiation and, more particularly, to a terahertz imaging system that includes a source array and a detector that distinguishes among the electromagnetic waves transmitted by the source array.
2. Background Information
Terahertz wave imaging has generated wide interest in the past decade due to the unique advantages of terahertz radiation. Many imaging technologies in the terahertz frequency range have been developed since the first raster scanning terahertz image was reported. Terahertz wave imaging has been used in various applications, such as security sensing and quality control inspection, for example. Terahertz wave two-dimensional (2D) imaging technology has been demonstrated using pulsed terahertz waves and continuous wave (CW) terahertz radiation. In contrast to a raster scanning imaging system, a 2D imaging system dramatically reduces the time required for image acquisition. It can also support real-time terahertz wave imaging in the above applications. However, the development of 2D terahertz imaging systems has been hindered by several problems. One problem is that current 2D terahertz wave detector arrays currently suffer from low sensitivity. Another problem is that integrating some terahertz wave detectors, such as the heterodyne detector, is difficult where a large number of pixels is desired. A third problem is that dilution in the terahertz wave's intensity over the entire 2D detector array causes current 2D terahertz imaging systems to have low signal-to-noise ratios.
A typical active imaging system is presented in FIG. 1, wherein a point source is used to provide the carrier wave for imaging. The electromagnetic wave from the point source is expanded by a lens and illuminates the entire target. An imaging lens is used to project the image of the target onto a detector array, which is either a film or a charge coupled device (CCD) detector for an optical image. A well-known imaging equation, 1/dt+1/dd=1/Fi, shows the relationship among the distances from the imaging lens to the target (dt), the imaging lens to the detector array (dd) and the focal length of the imaging lens (Fi). The magnification of the imaging system, M=|dd/dt|, gives a ratio between the dimensions of the image and the target.
However, this imaging system structure of FIG. 1 cannot be applied in an imaging system in the terahertz frequency range because there is currently no suitable 2D detector array available for the signals in the terahertz frequency band. Therefore, known methods of 2D terahertz wave imaging utilize a single detector and raster scanning of each pixel of the image across the detector.
Thus, a need exists for a two-dimensional terahertz imaging system that acquires an image of a targeted object more quickly than a raster scanning imaging system and that does not require a two-dimensional detector array.